Polymerization of mono- and polymethylstyrene



'tlrtited rates Faterrt i 3,058,968 FOLYMERHZATION F MONO- AND POLYWTHYLSTYRENE Frederick J. Soderquist, Essexviile, Harold D. Boyce, Coleman, and James L. Amos, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Dec. 21, 1959, Ser. No. 860,688 6 Claims. (Cl. 260-935) The present invention relates to a method for polymerizing monoand polymethylstyrenes, and is more particularly concerned with polymerizing said methylstyrenes in a ball mill polymerizer.

The polymerization of methylsty-renes has been hampered by the formation of cross-linked particles, or gels, which foul the equipment and result in loss of product and the time which is required to clean equipment before operations can be resumed.

We have now found that methylstyrenes may be polymerized either batchwise or continuously with essentially no gel formation for indefinite periods of time. Furthermore, if a slight gel formation does occur, it is present in the form of a readily filterable fioc which does not plug the equipment and is easily removed from the desired product.

According to our invention monoand polymethylstyrenes are polymerized by charging said methylstyrenes into a rotating ball mill which is maintained at a polymerizing temperature of from about 90 to about 150 C., and which contains from about 4 to about 12 volume percent, preferably from about 7 to about 9 volume percent of spheroidal objects of at least two different sizes or densities, said densities being between about 4.0 and about 10.0 g./cc. We have further found that the spheroids must be of such size as to form not less than 3 continuous rows across the length of the ball mill, with the larger balls, or balls having a greater density forming at least one row, and that the number of smaller balls, or balls having a lower density, should be not less than A,, and preferably not less than /2 the number of larger balls.

The actual size of the balls will be determined by the size of the ball mill, by the viscosity of the polymerizing mixture in the mill, and by the rotational speed of the mill, but should not exceed 3 to 4 inches in diameter in any case. In operation it is necessary that the smaller or lighter balls be of such weight that they will be carried part way up the wall of the ball mill and then fall back into the mass of larger balls, thus displacing the larger or heavier balls in a transverse direction and preventing the larger or heavier balls from tracking. When tracking, that is, following the same path around the drum, they allow gel formation between the respective tracks. This weight will be determined by the rotational speed of the mill and the viscosity of the polymerizing mixture. While it is necessary that at least two different sizes or weights of balls be used the invention is not limited thereto. Three or more sizes or weights of balls may be used to obtain the same results as long as the above mentioned proportions and conditions are met.

We have found that peripheral drum speeds of 5 0 to 100 feet per minute are satisfactory, with speeds of 64 to 72 feet per minute being preferable. Polymer conversion may be carried to from to 50 percent completion, desirably to from about 35 to about 45 percent. The organic content of the mill should be in the range of 32.0 to 570 volume percent for optimum operation. Any temperature from 90 to 150 C. may be used, although temperatures of from 120 to 130 C. are preferred. If it is desired to operate under superatmospheric pressure higher temperatures may be employed.

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The present invention may be better understood, but is not to be construed as limited by the following exarnples:

Example I A ball mill 9 inches long and 6 inches in diameter was rotated at a speed of 41 to 46 rpm, i.e. 64 to 72 feet per minute peripheral drum speed, while partially immersed in a constant temperature bath at a temperature of and C. The mill contained 20 stainless steel balls /2 inch in diameter, 22 stainless steel balls inch in diameter, and 22 stainless steel ball-s 1 inch in diameter. This amounted to 5.3 continuous rows of balls and a total volume of about 7 percent of the volume of the drum. The steel balls had a density of from 7.0 to 8.0 grams per cc. A composition of 95 percent of a mixture of metaand para-vinyltoluene and 5 weight percent of a mixture of 0-, mand p-diethylbenzene was fed into the mill at a rate of 300 grams per hour through a suitable axial inlet port. Product was removed continuously through an outlet port. Operation was continued for 578 hours and resulted in the formation of only 10 grams of dry filterable floc. There was no build up of gels on surfaces within the polymerizer. The material recovery was 93.8 Weight percent having an average polymer content of 41.4 percent.

Example 11 The experiment of Example I was repeated omitting the steel balls entirely and increasing the feed rate to 329 grams per hour to duplicate the residence time. After 775 hours copious quantities of gels had formed on surfaces within the polymerizer necessitating a shut down for cleaning the equipment.

Example IV Experiments were conducted with less than 3 rows of balls and again the gels began to form and build up. When 10 rows of balls were used (14 volume percent) the mass of balls remained on the bottom with little or no action. Similarly, when only one size of ball was used the balls tended to track and form ridges of gels around the walls of the mill.

Similar results are obtained by duplicating the foregoing procedures in a batchwise fashion, i.e. charging the desired monomer into the ball mill which is rotated, while being heated at a selected temperature, tmtil the desired polymerization has occurred, and then removing the organic contents of the ball mill for further process- Various modifications may be made in the present invention without departing from the spirit or scope thereof, and it is understood that we limit ourselves only as defined in the appended claims.

We claim:

1. A process for polymerizing -ar-monoand polymethylstyrene which comprises charging said methyl styrenes into a rotating ball mill which is maintained at a polymerizing temperature, and which contains from about 4 to about 12 volume percent, and not less than 3 continuous rows, of spheroids of at least two different weights, with the balls of greater mass forming at least one row and the number of balls of smaller mass being not less than the number of balls of greater mass, and rotating said ball mill at a peripheral speed of 50 to 100 feet per minute thus carrying the balls of smaller mass up the wall of the ball mill to a position from which they fall back into the polymerizing mix- )11116 and displace the balls ofrgreater mass to a new position in the continuous row of balls, thereby preventing tracking.

2. The process of claim' 1 wherein the polymerization is carried out in a continuous manner. 7

3. The process of claim 2 wherein the methylstyrene is vinyltoluene.

4. The process of claim 3 wherein the temperature is maintained at from 90 to about 150 C.

5. The process of claim 4 wherein the spheroids are stainless steel balls of at least two different sizes.

6. The process of claim 5 wherein about 7 volume percent of the steel balls are employed, forming about 5 rows of said balls in said rotating ball mill.

References Cited in the file of this patent UNITED STATES PATENTS 2,479,360 Howard Aug. 16, 1949 2,779,752 Vining Jan. 29, 1957 2,856,272 Baeyaer-t Oct. 14, 1958 7 OTHER REFERENCES Boundy-Boyer: Styrene, pp. 123741 (1952), Reinhold Publishing Corp., New York, NY. 

1. A PROCESS FOR POLYMERIZING AR-MONO- AND POLYMETHYLSTYRENE WHICH COMPRISES CHARGING SAID METHYL STYRENES INTO A ROTATING BALL MILL WHICH IS MAINTAINED AT A POLYMERIZING TEMPERATURE, AND WHICH CONTAINS FROM ABOUT 4 TO ABOUT 12 VOLUME PERCENT, AND NOT LESS THAN 3 CONTINUOUS ROWS, OF SPHEROIDS OF AT LEAST TWO DIFFERENT WEIGHTS, WITH THE BALLS OF GREATER MASS FORMING AT LEAST ONE ROW AND THE NUMBER OF BALLS OF SMALLER MASS BEING NOT LESS THAN 1/3 THE NUMBER OF BALLS OF GREATER MASS, AND ROTATING SAID BALL MILL AT A PERIPHERAL SPEED OF 50 TO 100 FEET PER MINUTE THUS CARRYING THE BALLS OF SMALLER MASS UP THE WALL OF THE BALL MILL TO A POSITION FROM WHICH THEY FALL BACK INTO THE POLYMERIZING MIX-TURE AND DISPLACE THE BALLS OF GREATER MASS TO A NEW POSITION IN THE CONTINUOUS ROW OF BALLS, THEREBY PREVENTING TRACKING. 